1. Field of the Invention
The present invention relates to a cathode ray tube having a lightweight funnel and a lightweight panel.
2. Description of the Related Art
A schematic appearance of a cathode ray tube is shown in
FIG. 6. In FIG. 6, D (mm) shows a diagonal axis length which is an effective dimension of a diagonal axis defined in EIAJ ED-2136A of the Standard of Electronic Industries Association of Japan.
FIG. 7 is a view showing a method of setting a diagonal axis length D of the cathode ray tube. In FIG. 7, a method 1 and a method 2 are shown. The method 1 can provide an effective shape (W, H, D: effective lengths of a major axis, a minor axis, and a diagonal axis shown in FIG. 6 respectively) by adding a 30-degree length of an blend R of an inner wall surface to the center position of the blend R of the inner wall surface, while using an R shape of a corner portion and a center position of the R shape of the panel inner wall surface (IL, IS, ID: center positions of the blend R of the panel inner wall surface in respective sectional shapes along the major axis, the minor axis, and the diagonal axis shown in FIG. 6 respectively). The method 2 can provide an effective diameter by using a contact point P of an inner curved surface Z=f(x,y) and the blend R, as shown in the right side in FIG. 7.
A sectional shape taken along an A-Axe2x80x2 line in FIG. 6 is shown in FIG. 8. In FIG. 8, 1a denotes a panel; 11, a face surface which is formed on the panel 1a and has a substantially square outer shape and on which the image is displayed; 12, a blend R portion of an outer wall surface; 13, a skirt portion which extends substantially vertically from all areas of an outer peripheral portion of the face surface 11 to the face surface 11; 1b, a funnel which has a funnel shape whose outer shape of a widest open portion of the funnel shape has the same outer shape as the skirt portion 13 of the panel 1a; 14, a sealing portion for connecting the panel 1a and the funnel 1b; 121, an F0 point which is located in the neighborhood of a joint between the blend R portion 12 and the face surface 11; 122, an F1 point which is located in the neighborhood of a joint between the blend R portion 12 and the skirt portion 13; 18, a neck portion which is a part of the funnel 1b and into which the electron gun is installed; 17, a yoke portion which is a part of the funnel 1b and onto which a deflection yoke for deflecting electron beams is fitted; 15, a body portion which is a part of the funnel 1b as shown in FIG. 8 and extends to the sealing portion 14 connected to the panel; and 16, a TOP OF ROUND which is an inflection point on a boundary line between the yoke portion 17 and the body portion 15 and is located at a position remote from a yoke reference line by 40 to 50 mm in the sealing portion direction. In this case, the yoke reference line is a reference line in a tube axis of the funnel, which is set forth in EIAJ ED-2134B.
As for the shape of the funnel 1b, respective dimensions of the sectional shape of the funnel 1b shown in FIG. 9 are given in Table 1 as an example.
The outer shape of the funnel 1b shown in FIG. 9 is connected smoothly from the neck portion 18, which is formed as a pipe shape of less than xcfx8640 mm in parallel with the tube axis direction, to the cone-shaped yoke portion 17, to which the deflection yoke is fitted and which is formed smoothly by using several R-shapes, and then connected to the sealing portion 14 via the TOP OF ROUND 16.
Normally, if the glass bulb consisting of the panel 1a and the funnel 1b is designed, a maximum tensile vacuum stress which is generated when an inside of the glass bulb is made vacuous is decided from a viewpoint of reliability, especially a viewpoint of the delayed fracture performance, and then a thickness is decided by using the stress as a threshold value. In addition, portions at which the vacuum stress is generated to cause the reduction of the reliability are located in the neighborhood of the blend R portion 12 of the face surface 11 of the panel, and in many cases such vacuum stress is generated mainly on the F0 point 121 or the F1 point 122 which is located within a width of 20 mm from both end positions of the blend R.
First, thicknesses at the F0 point 121 and the F1 point 122 are decided in view of the maximum vacuum stress. Then, a thickness distribution of the skirt portion 13 is decided such that the crack of the glass, etc. are not generated in the heating process step contained in manufacturing steps of the glass bulb. Accordingly, thicknesses up to the sealing portion 14 are decided, whereby the thickness design of the panel 1a can be completed.
Then, a thickness of the funnel 1b is decided based on the thickness of the sealing portion 14, whereby the shape design of the funnel 1b can be completed. That is, thicknesses of the body portion 15 and the yoke portion 17 are decided according to the thickness of the sealing portion 14 to be connected smoothly to the neck portion 18.
For example, as for the aperture grille type cathode ray tube which has the panel 1a whose diagonal axis length D is 410 mm and to which a physically reinforcing layer is applied, and in which the maximum value of the stress generated on a surface of the panel 1a when the inside of the glass bulb is made vacuous is less than 8.85 MPa, and in which an outer shape R of the face surface 11 is about more than R 30000 mm, the center thickness of the panel 1a is set to about 12 mm, the width of the sealing portion 14 is set to about 9 mm, and the thickness of the body portion 15 is set to about 5.4 mm at the lowest minimum in the range from the B-Bxe2x80x2 sectional shape to the C-Cxe2x80x2 sectional shape of the body portion 15 shown in FIG. 8.
In this case, the B-Bxe2x80x2 sectional shape is located at a position which is a half of the funnel body portion in the height direction. Also, a sectional shape which is located just in the middle of the B-Bxe2x80x2 sectional shape and the TOP OF ROUND to divide the height into two parts is set as the C-Cxe2x80x2 sectional shape.
Thickness data of the glass bulb shape every diagonal axis length D are set forth in Table 2.
Here, the center thickness means a center thickness of the panel 1a, the sealing surface thickness means a thickness of the sealing portion 14, and the body portion center thickness means a minimum value of the thickness (here, the thickness on the minor axis) in the range from the B-Bxe2x80x2 sectional shape to the C-Cxe2x80x2 sectional shape (positions corresponding to 50 to 75% of the length of the funnel body portion 15 along the tube axis direction) of the body portion 15 shown in FIG. 8.
In the structure of the cathode ray tube in the related art, since the design is carried out in light of several points such as the blend R portion 12, etc., such design depends largely upon the experience of the designer and thus the cathode ray tube has the unnecessary thickness which is naturally unnecessary. In particular, the cathode ray tube having a flat panel face tends to increase the thickness, and thus a weight of the cathode ray tube becomes heavy.
The present invention has been made to overcome the above subjects, and it is an object of the present invention to provide a lightweight cathode ray tube by detecting an optimal thickness of a funnel portion.
In order to achieve the above object, according to the present invention, there is provided a cathode ray tube comprising: a panel having a face surface whose outer shape is a substantial rectangle and a skirt portion which extends substantially vertically from all areas of an outer peripheral portion of the face surface to the face surface; a funnel which has a funnel shape whose outer shape of a widest open portion of the funnel shape has a same outer shape as the skirt portion of the panel; and a sealing portion for connecting the panel and the funnel, wherein the funnel comprises a body portion having a sealing surface which is connected to the sealing portion, a yoke portion connected to the body portion, and a neck portion connected to the yoke portion, and wherein the cathode ray tube includes a portion whose thickness becomes
(2.78+0.0038xc3x97D)xe2x89xa6t1xe2x89xa6(3.7+0.0038xc3x97D)[mm]
where D is a diagonal axis length [mm] between rectangular corner portions of an effective screen of the panel, and t1 is a thickness [mm] at positions which occupy 75% of a length of the body portion extending from the sealing surface of the body portion to the yoke portion along a tube axis direction.